Meiosis study Flashcards
What is meiosis?
Meiosis helps produce gametes and ensures genetic variation
- meiosis is a type of cell division in which the number of chromosomes is reduced by half (23 chromosomes)
Phases of meiosis?
Meiosis begins with a diploid cell and ends with 4 Hapliod cells
- Meiosis 1 begins after dna replication in inter phase (s phase)
- both meiosis 1 and 2 go through the same 4 phases of mitosis
Prophase
Metaphase
Anaphase
Telophase
what happens in meiosis 1
prophase 1?
nuclear envlope breaks down, chromosomes condens, and centioles move to opposite poles of the cell, and a spindle begins to form
- chromosomes pair up in homologous chromosomes and crossing over occurs during prophase 1
What are homologous chromosomes?
Homologous chromosomes is a pair of chromosomes that are similar in size, shape, and genetic content
What is crossing over?
Crossing over is when homologous chromosomes exchange segments of dna and this results in genetic variation
What happens in meiosis 1
Metaphase 1?
Metaphase 1= spindle fibers attach to the paired homologous chromosomes, and they line up along the metaphase plate
What happens in Meiosis 1
Anaphase 1?
Anaphase 1= spindle fibers shorten and the chromosomes of each homologous pair start to separate and move to opposite poles of the cell
What happens in meiosis 1
Telophase 1 and cytokinesis?
Telophase 1 and cytokinesis= spindle breaks sown and new nuclear membrane forms
- the cytoplasm of the cell divides and 2 haploid daughter cells each have a random assortment of chromosomes and 1 from each homoglous pair
- go onto meiosis 2 the dna doesnt replicate between meiosis 1 and 2
What happens in meiosis 2
Prophase 2?
Prophase 2= nuclear envelope breaks down, spindle forms in each haploid daughter cell, and the centrioles seperate and move to oppposite poles
What happens in meiosis 2
Metaphase 2?
Metaphase 2= spindle fibers line up sister chromatids of each chromosome along the metaphase plate of the cell
What happens in meiosis 2
Anaphase 2?
Anaphase 2= sister chromatids seperate and move to opposite poles of the cell
What happenes in meiosis 2
Telophase 2 and cytokinesis?
Telophase 2 and cytokinesis= spindle breaks down, new nuclear membrane forms, cytoplasm of the cell divides, and 4 haploid cells result which each has a unique combination of chromosomes
- 4 haploid cells are not identical to the parent cell or to each other because of the different alleles and crossing over
What does synapsis mean?
Synapsis is when homologous chromosomes pair up
-when the tetrad pairs up
What is the difference between meiosis 1 and 2
meiosis 1 separates pairs of homolgous chromosomes and meiosis 2 makes sure that 1 copy of each chromatid is in each of the 4 haploid cells
What happends to homolgous chromosomes after crossing over?
Homolgous chromosomes are not identical after crossing over because they now contain different alleles and genes
3 reasons for why we have genetic variation?
Crossing over, random fertilization, and independent assortment
- meiosis produces offspring that are different to protect them against diseases
What is independent assortment?
How your chromosomes were sorted independently
What is random fertilization?
It’s almost impossible for a sperm and egg cell to create genetically identical people
What is a tetrad?
Duplicated homologous chromosomes
What is nondisjunction?
The failure of 1 or more pairs of homologous chromosomes or sister chromatids to seperate
- leads to some daughter cells having too much or too little chromosomes
What caused Down syndrome?
Due to having 1 extra copy of chromosomes in trisomy 21, and this leads to Down syndrome because there are 3 copies of chromosomes instead of 2
What are deletions?
Chromosome segment lost
What are translocation?
Segment from chromosome is transfers to another chromosome that doesnt need it
What are duplication?
Segment from 1 chromosome is transfers to its homolgous chromosome giving it a duplicate of genes
